# CVE-2026-12340: Out-of-bounds heap read in SM2/SM3 certificate Subject Key Identifier computation

> An out-of-bounds heap read in wolfSSL's SM2/SM3 certificate verification can cause a denial of service when processing malformed public keys.

- **Severity:** Medium 6.3 (`CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 25 Jun 2026
- **Updated:** 26 Jun 2026
- **Also known as:** DEBIAN-CVE-2026-12340, GHSA-q349-x427-xg3w, JLSEC-2026-700, UBUNTU-CVE-2026-12340

## What is CVE-2026-12340?

CVE-2026-12340 is a medium-severity memory corruption vulnerability in Wolfssl Wolfssl, published on 25 Jun 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

Out-of-bounds heap read during SM2/SM3 certificate signature verification. When parsing a certificate with an SM3wSM2 signature, the Subject Key Identifier computation reads the trailing 65 bytes of the public key without checking that the key is at least that long. A public key shorter than 65 bytes results in an out-of-bounds heap read, leading to a potential crash (denial of service); there is no out-of-bounds write. Note this only affects builds with SM2 support (--enable-sm2 or --enable-all).

Weakness: CWE-125 (Out-of-bounds Read)

## Which versions are affected by CVE-2026-12340?

It affects 1 product.


Products: Wolfssl Wolfssl.

## How do I fix CVE-2026-12340?

Apply the vendor's patch.

## Is CVE-2026-12340 being exploited?

There is no known exploitation of CVE-2026-12340 in the wild and no public exploit code.

## Other vulnerabilities in Wolfssl Wolfssl

- [CVE-2024-5991](https://insights.sbomify.com/CVE-2024-5991/): Buffer overread in domain name matching (critical 10.0)
- [CVE-2021-37155](https://insights.sbomify.com/CVE-2021-37155/): Security feature bypass in n/a (critical 9.8)
- [CVE-2020-36177](https://insights.sbomify.com/CVE-2020-36177/): Memory corruption in n/a (critical 9.8)
- [CVE-2014-2896](https://insights.sbomify.com/CVE-2014-2896/): Memory corruption in n/a (critical 9.8)
- [CVE-2014-2897](https://insights.sbomify.com/CVE-2014-2897/): Memory corruption in n/a (critical 9.8)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-12340 and fix it if it is affected.

What it is: CVE-2026-12340 is a medium-severity memory corruption vulnerability in Wolfssl Wolfssl, published on 25 Jun 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-12340 in the wild and no public exploit code.

Affected product: Wolfssl Wolfssl. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-12340/ (Markdown: https://insights.sbomify.com/CVE-2026-12340/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-12340
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-12340
- OSV: https://osv.dev/vulnerability/CVE-2026-12340

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-12340/
Summaries are generated and may contain mistakes; the official description above is the record.